It's not unusual to question your poor life choices after you slip into a food coma. "Why didn't I stop after my first slice of pizza?" "Did I really need three plates of Thanksgiving dinner?"
But according to researcher Fred Provenza, food comas are about a lot more than just overeating: Your body might actually be sending you important signals about the nutrients and toxins in the meal you just ate. And you need to start listening.
Provenza, a professor of ecology at Utah State University, came to this insight after dozens of experiments in animals over the past three decades. The technical term for a food coma or food hangover is "negative post-ingestive feedback" — and it's just one part of the "nutritional wisdom" that he contends all creatures are born with, including humans.
In order to study this nutritional wisdom, Provenza would make goats, sheep, or cattle deficient in some dietary element and see if they'd seek out foods that were rich in the minerals or nutrients they were missing. The animals would indeed often opt for foods with flavors associated with whatever they were lacking — a sign that they could use flavor as a guide for their nutritional needs.
Unfortunately, this is harder for humans. In the age of mass agriculture, Big Food, and food comas, we've become unlinked from our natural food landscapes. Much of what we eat is infused with artificial flavors divorced from their actual nutritional value. Provenza thinks this has hijacked the body's ability to know what it needs and how to get it.
Over the last five years, he has been trying to figure out what his research in livestock and wild animals can tell us about where people go wrong — results he'll publish in a soon-to-be released study in the journal Appetite.
He previewed some of his research with Vox, explaining why he thinks humans falter with food, how all creatures — from insects to birds and mammals — have a wisdom of the body that helps them select foods to stay healthy, and what this can tell us about everything from food hangovers to obesity.
Julia Belluz: "Nutritional wisdom" sounds a bit hokey. What is it?
Fred Provenza: Forty or 50 years ago, there was no belief that there was a nutritional wisdom of the body, especially in domestic animals. If you talked about nutritional wisdom in those days, you would be shot down, humiliated. The idea was that 10,000 years of domestication had eradicated any sort of nutritional wisdom in animals.
But then I started watching animals, like goats. I'd notice they'd avoid new [plant] growth, for example, and wonder why they were avoiding something that appears to be most nutritious. They ate unusual foods that rectified nutritional deficiencies they were experiencing. What was clear to me was that there was more going on than meets the eye. But the challenge was: How do you scientifically demonstrate animals have nutritional wisdom?
We came up with a very simple idea. First off, we'd make the animals mildly deficient — in energy, protein, or minerals. Then we'd see if they would select for flavored food that would help their recovery from the deficiency. We were able to show, over and over, that they did.
JB: Can you describe these experiments?
FP: We would take a food that doesn't have much nutritional value, like straw. We'd have two groups of animals. On day one, in one group, the animals would get an hour-long meal with straw that had a maple flavor. Another group would get straw with an apple flavor. After the meal, we would take a stomach tube and pour a liter of water into the stomach of the animals.
The next day, we would offer animals a meal again, and we’d switch the flavors. After that meal, we'd feed the animals the nutrient they were lacking, directly into their gut through a tube.
Then we’d ask the animals which flavor they preferred when they were deficient in that nutrient, giving them a choice between the two flavors of straw. We found over and over and over again that the animals would form a strong preference for the flavor they’d eaten just prior to when we’d feed them the nutrient they were deficient in.
JB: Human studies have come to similar findings, as you know. For example, if you take babies that are deficient in some nutrient, they select foods that could help give them what they need — even cod liver oil. Yet today food hangovers are part of everyday life for many people. We almost expect to feel bad after eating, and we've eaten ourselves into a global obesity crisis. How did humans become so divorced from these instincts you found were common in animals?
FP: The junk food industry has created artificial flavors and linked them with energy-rich refined carbohydrates like high-fructose corn syrup. That combination conditions strong preferences. So while the flavors of produce, meat, and dairy have become blander over time, processed foods have become more desirable. People have learned to link synthetic flavors with feedback from energy-rich compounds that obscure nutritional sameness and diminish health. (For more on this, see here.)
In today's food culture, we've lost things that used to guide us nutritionally. We no longer grow our own meats and produce, and the culture in which we live no longer guides us in healthy ways nutritionally.
I think the obesity problem is multifaceted. The lack of availability of nutrient-rich foods has adversely influenced our food selection. When it comes to fruits and vegetables and meats, we have selected for yield as opposed to nutritional richness. So that alone causes a person to over-ingest to try to meet nutrients in short supply.
JB: How do you make sense of all the cravings people have for junk food?
FP: There's not a huge scientific literature out there on this idea in humans. In herbivores [vegetarian creatures], one thing that’s pretty clear is that when they are selecting a diet, if they’re not deficient, they’ll eat a variety of foods meal to meal, day to day, which ensures they ingest a variety of forages that vary in phytonutrients. But there won’t be a strong selection in a particular direction.
When they become deficient, however, they start to respond strongly. When the body needs more of something than what it's getting, strong cravings kick in.
I think cravings are very meaningful. If people are eating wholesome foods and they are experiencing cravings, it is the body guiding a person to select what's needed at the cellular level. Post-ingestive feedback, which changes liking for flavors of foods, is cells and organ systems guiding us in terms of what they need.
The curveball comes in when you get on junk foods, foods high in refined carbs. First, compounds they contain like sugar can be addictive. Second, if you're on a diet that is high in refined carbs, high in energy-dense processed foods, you can end up overeating in an attempt to get nutrients in short supply. That, of course, leads to over-consumption of energy, which the body stores as fat.
JB: In your research, you talk about "post-ingestive feedback," which sounds a lot like today's food hangover or food coma.
FP: Feedback can range along a continuum from satiety [feeling satisfied] to surfeit to malaise, including nausea. Excesses and deficits of nutrients cause malaise, as do excesses of toxins.
JB: Why do you think some people are more in touch with their post-ingestive feedback than others?
FP: I think some people are simply more mindful, and thus aware of how they feel, than others. Of course, we can cultivate mindfulness and awareness in all we do, including eating.
JB: Any advice for how people can avoid food hangovers?
FP: Eating a variety of wholesome foods, paying attention to the flavors of those foods and the sensations of the body during and after a meal. For many people, especially people who are on a diet of junk food, committing to eating only wholesome foods for several weeks and then going back to the junk food can provide a dramatic contrast that illustrates how both kinds of foods taste and feel. For most people, they will no longer like the taste or feedback they experience from junk foods.
JB: Did your research change your own eating patterns?
FP: For my wife and my family, to an amazing degree, it changed how we looked at foods and feeding and thinking about the importance of what the body is telling you.
For most of our evolutionary history, there was no such thing as nutritionists, pharmacists, or medical doctors — the body was all of those things.
It's evolved over time for my wife and me, but we try to shop and eat mindfully, avoid bringing home junk, try to select the most wholesome foods. Let the body guide our choices, day to day, meal to meal. And not worry about anything beyond that. Just leaving it up to the body, but doing that by bringing home really wholesome foods.